The present invention relates to novel pressure-sensitive chromogenic copy systems and receptor sheets and transfer sheets therefor, as well as novel compositions for use as color developers.
The use of aromatic carboxylic acids in carbonless copying systems has been known in the art for a long time, and is described, among others, in U.S. Pat. Nos. 3,488,207, 3,682,680, 3,772,052, 3,871,900, 3,896,255, 3,900,215, 3,934,070, 3,983,292, 4,303,719, 4,374,671, 4,372,583, 4,559,242, and 4,631,204. The salicylates, their metallic compounds and other salicylate derivatives including oligomers of salicylates and their metal compounds, appear to offer the best overall properties as image developers in carbonless systems. The rather complex manufacturing methods known to date for producing salicylates and the associated relatively high cost, however, has prevented any significant use of such materials in carbonless copy systems on a commercial basis.
It has now been discovered that a number of changes in the conventional production methods of salicylates can be made which changes result in a significant reduction of the manufacturing costs of these salicylates without diminishing their desired properties as color-developing materials in carbonless papers. These new processing methods are applicable to all the known syntheses reactions for manufacture of salicylates and salicylate derivatives, and can yield materials with attractive and competitive cost structure which can result in a widespread use of these compounds in the carbonless paper industry. Additionally, the new processing methods afford color developing materials which possess significantly improved properties (image intensity, speed of image formation, and image stability) over materials known in the prior art.
One of the commonly-used methods for producing salicylates is the well-known Kolbe-Schmitt reaction (Schmitt, J. Pract. Chem., [ii], 31,397 (1885)), whereby the sodium salt of a phenol is heated with carbon dioxide under pressure at a temperature of between 130-140.degree. C. Another method for manufacturing salicylates is described by W. Meek and C. Fuschman in the Journal of Chemical and Engineering Data, (Vol. 14, No. 3, July 1969, p. 388) whereby carboxylation of substituted phenols is performed under atmospheric conditions and with the use of N,N'-dimethylamide solvents to produce substituted salicylates in superior yields.
Still another method for manufacturing salicylates of the present invention is the combination of the two aforementioned manufacturing methods, i.e., the use of solvents in combination with the use of pressurized environments of varying temperatures.
Irrespective of the manufacturing method used, the salicylates must be processed extensively; i.e., they must go through steps such as layer separation (if a solvent is used), purification (often repeated purification steps involving counter-current extractions), precipitation of the alkali salt of the salicylate to obtain the free acid by acidifying the aqueous layer containing the salicylate salt, filtration, and drying.
If the salicylate or salicylate derivative is to be used as a color developer, the carbonless system manufacturer must process the material further to incorporate it into a coating and apply it to the color-developing substrate. Such further processing by the carbonless manufacturer may involve steps such as grinding, dissolution, mixing with pigments and binders, and, optionally, the formation of a polyvalent metal salt of the salicylate.
All the aforementioned processing steps by the manufacturer of the salicylate and the manufacturer of the final carbonless product render the use of salicylate and salicylate derivatives economically unattractive.